Create app.py

app.py

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+# app.py
+# This is the main file for our FastAPI application.
+
+import io
+import sys
+from fastapi import FastAPI, HTTPException
+from pydantic import BaseModel
+from fastapi.middleware.cors import CORSMiddleware
+
+# Initialize the FastAPI app
+app = FastAPI(
+    title="Python Code Executor API",
+    description="An API to execute Python code securely and return the output.",
+    version="1.0.0",
+)
+
+# --- CORS Middleware ---
+# This is important to allow your front-end website (running on a different domain)
+# to communicate with this API. We'll allow all origins for simplicity.
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],  # Allows all origins
+    allow_credentials=True,
+    allow_methods=["*"],  # Allows all methods (GET, POST, etc.)
+    allow_headers=["*"],  # Allows all headers
+)
+
+
+# --- Request Body Model ---
+# This Pydantic model defines the structure of the JSON we expect in the request.
+# It ensures that the incoming data has a "code" field which is a string.
+class Code(BaseModel):
+    code: str
+
+
+# --- API Endpoint ---
+# This defines the endpoint at the path "/execute" that accepts POST requests.
+@app.post("/execute")
+async def execute_python_code(code_payload: Code):
+    """
+    Executes the provided Python code and returns its output or any errors.
+    """
+    # Create a string buffer to capture the output of the print() statements
+    old_stdout = sys.stdout
+    redirected_output = io.StringIO()
+    sys.stdout = redirected_output
+
+    try:
+        # The exec() function executes the Python code passed as a string.
+        # We pass an empty dictionary for globals and locals for a cleaner scope.
+        exec(code_payload.code, {}, {})
+    except Exception as e:
+        # If any error occurs during execution, restore stdout and raise an HTTPException.
+        # This will be sent back to the user as a proper error response.
+        sys.stdout = old_stdout
+        raise HTTPException(
+            status_code=400,
+            detail=f"Error executing code: {str(e)}"
+        )
+    finally:
+        # This 'finally' block ensures that we always restore the original stdout,
+        # even if an error occurred. This is crucial for the server's stability.
+        sys.stdout = old_stdout
+
+    # Get the captured output from the string buffer
+    output = redirected_output.getvalue()
+
+    # Return the captured output in a JSON response
+    return {"output": output}
+
+# A simple root endpoint to confirm the API is running
+@app.get("/")
+def read_root():
+    return {"message": "Python Code Executor API is running."}